The former under-treasurer Tim Marney is no stranger to controversy when calling successive state governments to account over their expenditure.

So it was no surprise his appointment as WA's new Mental Health Commissioner sparked debate when it was revealed he would continue to earn $429,000 a year in his new role.

His predecessor, Eddie Bartnik, received a salary of about $265,000 a year.

The State Opposition has described the salary as wasteful, but today Mr Marney told ABC Mornings he had been transferred within the public sector, at his request, and had 18 months left to run under his existing contract.

He also said the role had been expanded with the merging of the Mental Health Commission with the Drug and Alcohol Office.

"It's going from running one agency to two agencies, merging those together," he told Geoff Hutchison.

"Plus I spend 20 per cent of my time on the health system at the moment so those are fairly significant responsibilities that I think are very different to the previous mental health commissioner's responsibilities."

Mr Marney also outlined his own personal battle with anxiety and depression, describing having panic attacks during parliamentary committee hearings.

"That first year under the Gallop Government was a very tough year for a whole range of reasons," he said.

"I recall sitting in expenditure review committees alongside the treasurer at the time, Eric Ripper, and having panic attacks but having to mask it and just power through and take the pain basically internally and continue to function, because I was there to do a job."

Mr Marney says while his anxiety was not diagnosed until adulthood, he can now look back and see clear signs from when he was a child.

"It's a recurring thought or fear that you just can't shake," he said.

"You just keep looking for a solution but there isn't one, which is frustrating because your logic drives you to seek a solution to something that's illogical."